The modification and/or regulation of plant growth to provide beneficial effects is well appreciated by those in the agricultural art. Among the most well recognized classes of plant growth regulatory chemicals are plant growth stimulants. Plant growth stimulants can result in a number of biological manifestations including the stimulation of the extensive growth of intact plants; the germination of dormant seeds and the growth of dormant buds; the overcoming of the light requirement for flowering (in certain species); the overcoming of the requirement in certain species for vernalization for flowering; the stimulation of the mobilization of foods and minerals in seed storage cells; the causing of parthenocarpic fruit development, as well as the delaying of aging in leaves and citrus fruits.
The commercial application of plant growth stimulants has involved the treatment of a wide variety of species to effect a number of beneficial changes. Thus, these types of compounds have been applied to fruits such as pears, lemons, grapes and cherries to increase the size and/or amount of fruit developed; to vegetables such as asparagus, celery and lettuce to promote vegetative growth; to seeds of crops such as oats, peas, cotton, rye, soybeans and wheat to promote rapid emergence; and to ornamentals to produce earlier blooming or more profuse or larger flowering.
However, there are drawbacks associated with many of the plant growth stimulants, such as gibberellins (a naturally occuring product of the Gibberella fungus, this class of compounds also being found in higher plants) including high costs, detrimental "side effects", short duration of effect, and the like. Accordingly, it would be desirable to possess new compounds which would function as plant growth stimulants and which would overcome one or more of the shortcomings of presently employed plant growth regulants.
The use of 1,3,4-oxadiazoles as pesticides is known in the art. Thus, U.S. Pat. No. 4,654,330 to Plant et al shows that certain of the substituted 1,3,4-oxadiazoles employed in the method of this invention are active as insecticides, nematocides and acaricides. Somewhat similarly, South African patent application Ser. No. 708,460 shows dithiophosphate substituted-1,3,4-oxadiazoles which are active as acaricides. However, neither of these patents suggests or discloses that the compounds disclosed therein would exhibit plant growth stimulatory activity.
Moreover, there have been several disclosures in the past that certain 1,3,4-oxadiazoles exhibit plant growth regulatory activity of the stunting or dwarfing variety. Thus, Belgian Pat. No. 816,774 shows (1,1,3,3-tetrahaloethyl)-5-amino-1,3,4-oxadiazoles which are valuable for dwarfing barley, while U.S. Pat. No. 4,035,175 to Brouwer et al shows 2-(1,3,4-oxadiazol-2-yl) benzoic acids and derivatives thereof, the application of which will lead to dwarfing and cessation of terminal growth. Similarly, U.S. Pat. No. 4,210,762 to Howe shows 2,5-di(substituted)phenyl-1,3,4-oxadiazoles which result in stature reduction, while U.S. Pat. No. 4,259,104 shows certain 4- and 5-substituted 2-(aryloxymethyl)-1,3,4-oxadiazoles which exhibit plant growth retardation activity.
Plant growth regulatory activity has also been reported for various 1,2,4-oxadiazoles. Thus, U.S. Pat. No. 4,135,910 to Howe shows 1,2,4-oxadiazol-3-yl-benzoates which are useful as growth regulants while Japanese Patent Publication No. 57188-503 shows a 1,2,4-oxadiazolyl chlorobenzene compound which functions as a plant growth stimulant. Somewhat similarly, German Pat. No. 2,600,655 discloses a variety of diphenyl-substituted heterocyclic compounds, including oxadiazolyl compounds, which exhibit inhibitory plant growth regulatory activity.
Thus, it is completely unexpected that the 1,3,4-oxadiazole compounds could be found which would exhibit plant growth stimulatory activity.